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Use the force!
• Try to move the book in front of you by only
using your mind!
• Do the books obey your will?
Q: What would be required to actually
move the book?
Force
• What is force?
– Push or Pull
• It’s what causes “things” to accelerate
1000 kg
Velocity & Acceleration Review
Dis tance [m]
Velocity 
Time [ s]
D
T V
V
AT
Velocity [m]
Acceleration 
2
Time [ s ]
V
AT
Force
Velocity [m]
Acceleration 
2
Time [ s ]
What is Mass?
Force  mass  acceleration
[kg m]
N
2
[s ]
Newton is the unit of measurement for Force
Q: What is Mass?
• A: Mass is the amount of Matter – or
“stuff” an object has.
– Stuff is made up of all of the atoms within the
object.
Objects with mass don’t just
suddenly start moving
by themselves
An object with mass takes
effort to move!
If it’s already moving, it takes
effort to stop it from moving!
We call this resistance
to change: “Inertia”
Question
• What would happen to our rate of
acceleration if we increase mass?
F=M*A
How Mass Affects Acceleration
With NO Mass
Positive
Acceleration
Negative
Acceleration
With More
Mass
Velocity
Acceleration
Properties of Mass
• Mass has inertia
– Inertia: Resistance to the push / pull, or
Change of Motion
• Newton’s 1st Law of Motion:
– once in motion an object stays in _______ - unless acted
upon by another _______.
– An object at rest stays at ______ – unless acted upon by
another _______.
Property of Mass
F=M*A
Push/Pull = Object w/ Matter * Faster/Slower
Inertia is why an object
with more mass resists
the pushing of the force.
Resistance
Inertia
Inertia: What does this mean?
An object which is resting – or not going
anywhere – doesn’t want to move, or go
anywhere. It wants to stay put. It isn’t going
to start moving on its own. In order to get it
moving, I have to “push” it.
1000 kg
An object
at rest
Inertia: What does this mean?
An object
In Motion
An object which is moving doesn’t want to stop.
It wants to keep moving. In order for it to stop, I
have to “push” against it.
(Usually, friction does a pretty good job of doing
that. Imagine a large hockey puck on ice)
Inertia
Inertia is also resistance to the “Push”. It doesn’t
want to get moving – so it resists you. The more
mass you have, the more it resists you.
Notice that the object is resisting motion. It wants
to stay put as I push against it (force).
An object
Resists the
“Push/Pull”
1000 kg
In the next slide, you will
also notice that with less
mass it’s easier to start it.
Inertia
Notice that the object is resisting the push. It
wanted to stay put as I push against it (force).
Notice that with more
mass, the more it resists.
An object
Resists the
“Push/Pull”
3000 kg
Mo Mass, Mo Inertia
Inertia
Also notice that with more
mass it’s harder to stop it.
Notice that when the object is in motion, it
wants to stay in motion until I push against it
(force)
3000 kg
Mo Mass, Mo Inertia
Inertia
Notice that when the object is in motion, it wants
to stay in motion until I push against it (force).
Also notice that with less
mass it’s easier to stop it.
1000 k
Less Mass, Less Inertia
First Law of Motion
Recap:
• Every object that has mass
has inertia.
First Law of Motion
Recap:
• Inertia is the objects resistance to a
change in its motion, or resistance to
the “Push/Pull”.
– An object at rest will stay at rest unless
it is acted upon by a force.” (and the
opposite is also true).
First Law of Motion
Recap:
•MO MASS
MO INERTIA
If the force were to stay the same, what do
you think happens to our acceleration w/
different masses?
Distance
In other words, w/ less mass, it
doesn’t take as much effort to get
it moving; therefore, I can move it
farther in less time (faster).
½ kg
1kg
W/ Less
Mass
2kg
In other words, w/ more mass, it
takes more effort to get it moving;
therefore, it takes me more time to
move it farther (slower).
W/ More
Mass
Time
Demo: Skateboard + 3 diff. people
What do you think happens to our
acceleration w/ different masses?
Distance
Which one of these lines do you
think would represent a sports
car, SUV & Diesel Truck?
The Diesel truck would be the least steep line!
Less steep = less rate of acceleration.
Sports car would be the steepest line!
Steeper = more rate of acceleration.
The SUV would be the middle line!
Steepness of line is in the
middle = average acceleration rate.
Time
Manipulating the Force Formula
• By manipulating the force formula, we can
get 6 different scenarios of how an objects
acceleration rate can be affected by force.
F=M*A
Force, Mass & Acceleration
Phrases
• If I Keep my “pushing” (Force) the same:
– If I add more mass, I accelerate slower
– If I take off mass, I accelerate faster.
• If I Keep my Mass the same:
– If I push hard, I accelerate faster.
– If I push less, I accelerate slower.
• If I want to Accelerate at the same rate:
– If I increase my mass, I have to push harder.
– If I decrease my mass, I don’t have to push as hard.
If I Keep Force
Constant:
30 N
• If I have less mass, I accelerate faster.
– This is because I have less inertia.
1000 kg
¤ Force
= Mass
* Acceleration
30 N
To Keep Force
Constant:
30 N
• If I add more mass, I accelerate slower
– This is because I have more inertia.
3000 kg
¤ Force
= Mass
* Acceleration
30 N
If I Keep Mass
Constant:
30 N
• If I push hard, I accelerate faster.
30 N
1000 kg
Force = Mass
¤*
Acceleration
If I Keep Mass
Constant:
10 N
• If I push less, I accelerate slower.
1000 kg
Force = Mass
10 N
¤*
Acceleration
To Keep Acceleration
Constant:
10 N
• If I decrease my mass, I don’t have to
push as hard.
1000 kg
Force = Mass
10 N
* Acceleration
¤
To Keep Acceleration
Constant:
30 N
• If I increase my mass, I have to push
harder.
30 N
3000 kg
Force = Mass
* Acceleration
¤
To Keep Force Constant
F
Control
M
Manipulated
A
Responding
If I take off mass, I accelerate faster.
•20 N
•20 N
½ kg
1kg
40 m/s2
20 m/s2
Control
•20 N
2kg
10 m/s2
If I add more mass, I accelerate slower
To Keep Mass Constant
Control
M
F
Manipulated
A
Responding
If I push more, I accelerate more.
1kg
30 N
30 m/s2
1kg
20 N
20 m/s2
Control
1kg
10 N
10 m/s2
If I push less, I accelerate less.
To Keep Acceleration Constant
A
Control
M
Manipulated
F
Responding
If I decrease my mass, I don’t have to push as hard.
20 m/s2
20 m/s2
10 N
½ kg
20 N
1kg
Control
20 m/s2
2kg
40 N
If I increase my mass, I have to push harder.